Power tongs are used in well drilling to rotate tubular sections that are being threaded together or unthreaded There exist numerous patents on power tongs, including the following U.S. Pat. No. 5,144,868 to Feigel, U.S. Pat. No. 4,709,599 to Buck, U.S. Pat. No. 4,649,777 to Buck, U.S. Pat. No. 4,631,987 to Buck, U.S. Pat. No. 4,576,067 to Buck, U.S. Pat. No. 4,593,584 to Neves (equivalent to Canadian patent 1,235,111), U.S. Pat. No. 4,487,092 to Neves, U.S. Pat. No. 4,404,876 to Eckel, U.S. Pat. No. 4,350,062 to Farr et al, (equivalent to Canadian patent 1,125,737), U.S. Pat. No. 4,089,240 to Eckel, U.S. Pat. No. 4,084,453 to Eckel, and U.S. Pat. No. 2,879,680 to Beeman et al; and the following Canadian patents: 1,190,919 to Farr et al, 1,088,918 to Eckel 1,075,676 to Eckel, and 1,037,463 to Eckel.
All of these power tongs include a frame having arcuate front portions defining a throat, a ring gear mounted on the frame for rotation about a central axis, and a cage plate assembly mounted on either the frame or the ring gear for rotation about a central axis. The throat receives the tubular section to be rotated, and the cage plate and ring gear include die means for gripping the pipe. The ring gear and cage plate cooperate to rotate the pipe within the frame, which remains stationary. In these design, the ring gear was mounted for rotation on the frame. In a diversion from these designs, the inventor proposed the design of U.S. Pat. No. 9,010,219, in which a power tong is disclosed for rotating a pipe, the power tong comprising: a frame having a pair of arcuate front portions defining a throat for receiving the pipe; a cage plate assembly mounted for rotation on the arcuate front portions about a center of rotation, the cage plate assembly having an opening that is alignable with the throat; a ring gear mounted for rotation within, and supported by, the cage plate assembly about the center of rotation, the ring gear having an opening that is alignable with the throat; the ring gear cooperating with jaws mounted on the cage plate assembly for gripping the pipe upon rotation of the ring gear. It was mentioned in this patent that the ring gear might rotate on a bushing slide surface.